Trauma is one of the leading causes of death in the United States. The primary reason for the high mortality rate is the inability to maintain tissue oxygenation of the patient between the time of injury and time of surgery at a medical facility. The lack of oxygenation results in tissue damage, organ failure and death. Therefore, a major focus in treating traumatic shock is administering therapeutics providing as much oxygen as possible to internal tissues and organs of the patients.
An obvious approach to maintain oxygenation is blood transfusion. However, there are significant practical problems using blood in point of care treatment which make the routine use of stored human blood for use outside the medical facility impractical on a wide spread basis. Standard approaches to treat trauma primarily involve maintenance of intravascular circulating volume through administration of either isotonic, hypertonic, or hyperoncotic solutions. These treatments cannot uniformly increase oxygenation of internal tissues and organs enough to effectively prevent ischemia and organ failure.
As a consequence there is a major effort to develop hemoglobin based oxygen carriers (HBOCs) which are capable of restoring oxygen carrying capacity of trauma patients. HBOCs have a number of advantages over the use stored human blood, including a decreased chance of disease transmission, no immune reactivity, lack of a need for typing, and most importantly improved availability with decreased storage demands. A number of groups have developed HBOCs and several companies have conducted clinical trials to develop their hemoglobin based products as blood substitutes. Hemoglobin (HGB) isolated from human or animal blood, or a synthetically produced oxygen carrier, such as perfluorocarbon, are two types of blood substitutes that have been in clinical trials. Other red blood cell substitutes, have also been developed and characterized for use in patients. (See, for example, Red Blood Cell Substitutes, 1998, (Eds.) A. S. Rudolph, R. Rabinovici, and G. Z. Feuerstein, Dekker, New York, N.Y.). Such red blood cell substitutes may be used in conjunction with standard medical therapies, such as transfused blood or blood products. As a specific example, Enzon, Inc. (Piscataway, N.J.), has developed a polyethylene glycol (PEG)-modified bovine hemoglobin, abbreviated PEG-HGB. PEG-HGB is produced by a process in which strands of PEG are crosslinked to the surfaces of HGB molecules, for example, as disclosed in U.S. Pat. Nos. 5,386,014 and 5,234,903 to Nho et al.). Other specific examples include Hemopure™ and Oxyglobin (Biopure, Cambridge, Mass.). However none of these products have been established to produce significant increases in tissue oxygenation and none have received FDA approval, either because they are ineffective or produce significant toxicity.
Lack of suitable HBOCs has greatly hindered basic research into the physiology of tissue oxygenation and our understanding of the critical mechanisms involved in shock and its ensuing tissue damage. With regards to the HBOCs that have undergone clinical testing and produced significant toxicity, scarce information is available on the cause of these toxicities.
Thus, the methods for treating trauma induced hemorrhage are presently insufficient. While blood transfusion can restore oxygen to tissue and replenish lost circulating volume, use of blood as a means to treat hemorrhaging outside of medical facilities has significant practical problems. First of all there are generally limited quantities of blood available and for each person treated typing is necessary to prevent killing the patient through an immune reaction. However the most important problem in using blood to treat trauma patients outside of medical facilities is the storage and packaging constraints inherent in using this tissue. Thus, blood transfusions are not normally employed in point of care treatment of trauma patients.
In fact, the standard approaches to treat trauma primarily involve maintenance of intravascular circulating volume through administration of either isotonic, hypertonic, or hyperoncotic solutions. These approaches are intended to provide short term replenishment of circulatory volume and can also increase blood flow and hence oxygen delivery to tissues. However, when hemorrhage is severe, these treatments cannot uniformly increase oxygenation of internal tissues and organs enough to effectively prevent ischemia and organ failure. As a consequence, we have a high death rate from those individuals subject to severe trauma.
For years attempts have been made to develop hemoglobin based oxygen carriers (HBOCs) which are capable of providing oxygen to trauma patients. HBOCs have a number of advantages over the use stored human blood without many of the problems associated with using blood to treat trauma. These advantages include a decreased chance of disease transmission, no immune reactivity, lack of a need for typing, and most importantly improved availability with decreased storage demands. Ideally HBOCs should be able to bind oxygen and release it to needed tissues. It should be in a ready to use solution that is in a form that is stable for months under most environmental conditions especially those commonly encountered in point of care conditions in which trauma patients need treatment.
Over the years a number of attempts have been made to develop HBOCs as oxygen therapeutics using either native or recombinant human hemoglobin, modified forms of human hemoglobin or modified forms of hemoglobin from other species. Unmodified hemoglobin can be used as an oxygen therapeutic however it binds NOx and causes severe vasoconstriction and hypertension. As a consequence of its molecular weight, hemoglobin can cause significant toxicities, especially to the kidney where it clogs the glomerular apparatus. As a consequence, most hemoglobin's that have been tested in humans are modified to prolong their half life and reduce their toxicity.
It is an object of the invention to provide novel oxygen and carbon monoxide carrying and delivering molecules that can serve as blood substitutes and/or have therapeutic activity, and processes for the preparation of these molecules.
It is a further object of this invention to provide stabilized and virally inactivated hemoglobin and hemoglobin conjugates with water-soluble polymers useful as a therapeutic agents in transfusion medicine, the viral inactivation rendering the native hemoglobin and resulting hemoglobin formulations essentially free of transmissible infection agents. The conjugates are capable of delivering oxygen or carbon monoxide bound to the hemoglobin to tissues.